In recent years, solar cells for directly converting sunlight into electric energy have been a focus of attention as a replacement for existing power generation systems depending on fossil fuels.
Referring to FIG. 1, an encapsulant sheet 4 formed of a hot-bonding resin is placed on a surface of a surface side protective member 1 formed of glass or a transparent resin, and a plurality of solar cell devices 3 is placed on the sheet 4. Likewise, another encapsulant sheet 4 is placed on the solar cell devices 3, and a rear side protective member 2 formed of glass or a resin is placed on the sheet 4 to form a laminated body.
The stacked sheets are integrated by pressing the two protective members 1, 2 while melting the encapsulant sheets 4, 4. FIG. 2 shows a solar cell module finished by melting the encapsulant sheets 4, 4 such that the encapsulant sheets 4, 4 are integrated with the other members. Here, an encapsulant 4′ is formed by integrating the encapsulant sheets 4, 4.
Further, hot-bonding resin sheets used as the encapsulant sheets 4 are generally formed through extrusion or calendaring using T dies. Here, all of these hot-bonding resin sheets exhibit high thermal shrinkage. Thus, when hot-bonding resin sheets are used as the encapsulant sheets 4, the encapsulant sheet 4 can severely shrink when heated such that the solar cell devices 3 in the encapsulant sheets 4 can be displaced or damaged due to stress applied to the solar cell devices 3.
A hot-bonding resin sheet having low thermal shrinkage as disclosed in Patent Document 1 is well known in the art. Such a hot-bonding sheet exhibiting low thermal shrinkage is obtained by partially or completely melting a hot-bonding resin powder. The hot-bonding sheet obtained by partially or completely melting the hot-bonding resin powder has a lower thermal shrinkage than a sheet manufactured through extrusion using T dies or calendaring.
Thus, a problem of displacing or damaging the solar cell devices 3 due to shrinkage of the encapsulant sheets 4 of the solar cell can be solved when the hot-bonding resin sheet of Patent Document 1 is used as the encapsulant sheets 4 for solar cells.
In addition, Patent Document 2 also discloses a resin sheet, which is formed by stacking a resin layer containing a crosslinking agent and a layer free from any crosslinking agent to reduce thermal shrinkage.
[Patent Document 1] Japanese Patent Publication No. 2002-363507A
[Patent Document 2] Japanese Patent Publication No. 2009-4437A